Teenagers who abuse alcohol are more likely to make a rocky transition into early adulthood, Finnish researchers said, after conducting a large study of twins.

After analyzing longitudinal data on more than 3,000 twins, researchers at Indiana University focused on adolescent twins who were “drinking-discordant” — in other words, one drank and the other did not. Although past studies demonstrate the effect of adolescent alcohol use on early adult outcomes, the new study further isolates the effects of alcohol abuse from genetics and a shared home environment.

“Very few studies that control for expected influences of shared familial experience and shared genetic liabilities on drinking outcomes have been reported," said Richard Rose, professor emeritus in psychology and brain science at Indiana University, in a statement. "While there are many published studies documenting the association of adolescent drinking with adverse adult outcomes, none of these were genetically informative or supported causal inferences."

Among the possible outcomes for the twins at age 25 were substance abuse, poor health, physical symptoms, early onset of sexual activity, multiple sexual partners, life dissatisfaction, financial problems, lack of education.

Matt McGue, a psychologist at the University of Minnesota, said that the new study confirms that adolescent alcohol abuse leads not only to heavier drinking dependency in adulthood but problems across the spectrum of life. “Importantly, the negative outcomes associated with adolescent drinking are not, however, limited to problems with alcohol; early drinkers are also more likely to report physical health problems, educational and occupational difficulties, and relationship problems,” he said.

However, what remains unclear to scientists is why such associations arise, McGue said. “The basic issue is that individuals who drink early and often in adolescence are not a random subset of adolescents, and it may be that the factors that led these individuals to drink early — perhaps mental health problems, personality, or coming from a dysfunctional family — are the actual causes of the adverse adult outcomes with which adolescent drinking has been associated."

Yet, regardless of the root causes of alcohol problems among adolescents, Rose says the study at least eliminates some confusion from the mix. “To my knowledge, ours is the first prospective study of discordant twin pairs,” Rose said. “It is, accordingly, the first to evaluate whether the established association of adolescent drinking problems with adverse adult outcomes can be fully explained by shared genetic and environmental liabilities. Our data suggest not."

Source: Rose R, Winter T, Viken R, et al. Adolescent Alcohol Abuse and Adverse Adult Outcomes: Evaluating Confounds with Drinking-Discordant Twins. Alcoholism: Clinical and Experimental Research. 2014.